Overview
What is M20-grade concrete? The term M in M20 refers to "mix," whereas 20 is its compressive strength after 28 days of curing, i.e., 20 MPa or 20 N/mm2. In the present scenario in Nepal, M20-grade concrete is generally used for column and slab casting in RCC structures. In order to calculate the unit rate of M20 in Nepal, you need to consider two basic codes or norms.
- District rate in a running fiscal year to find the unit rate of materials and workers. Here we are taking the Kathmandu district rate for fiscal year 2079/80. You can find this rate on the Ministry of Physical Infrastructure Development website. http://tid.bagamati.gov.np/en/kathmandu
- Norms specified in the Department of Urban Development
and Building Construction (DUDBC) to calculate the number of workers per
unit of 20-grade concrete. You can find on the DUDBC website Bhawan Nirman
(Civil) Karyaharu ko darrate bislashand sambandhi norms in publications in
the media center menu. https://dudbc.gov.np/list/resource/192?parent=1874
We have broken down the calculation into these four headings to find the total cost per unit of M20-grade concrete.
- Calculation of the quantity of construction materials and cost
- Calculation of quantity of workers and cost
- Calculation of equipment and cost
- Contractor overhead and profit
Construction Materials Cost Analysis
Quantity calculation in M20-grade concrete in 1 cu. m
The mix proportion for M20 concrete is 1:1.5:3, i.e., 1 part of cement is mixed with 1.5 parts sand and 3 parts aggregate by volume.
The quantity of 1 cubic meter of concrete we are dealing with is a wet volume of concrete. We need to find material requirements for dry volume with the formula
Dry volume = wet volume * 1.54 to 1.57 the wet volume of concrete
This means the volume of concrete mix decreases when adding water to it by 54 to 57%. Normally, the value of 1.54 is taken.
Sum ratio for M20 = 1 + 1.5 + 3 = 5.5
Now, changing it to dry volume,
Dry volume = 1.54 * wet volume
= 1.54*1
= 1.54 cu.m
Let's find the quantity of each mix component.
Volume of Cement
= (ratio of cement/sum of ratio)*dry volume
=(1/5.5)*1.54
=0.28cu.m
Volume of Cement: 0.28 cu.m.
As cement comes in bags of 50 kg, let's find the bags of cement per cubic meter of concrete.
The cement density is taken as 1440 kg/m3.
Weight of Cement in kg = cement volume * cement density
=0.28*1440
Weight of Cement in kg = 403.2 kg
Number of cement bags = 403.2/50
=8 bags
Volume of Sand
= (sand ratio/total of ratio) * dry volume
=(1.5/5.5)*1.54
=0.42 cu.m
Volume of sand = 0.42 cu.m.
Volume of Aggregate
=(ratio of sand in mix / total sum of ratio in mix) * dry volume=(3/5.5)*1.54
=0.84 cu.m
Volume of aggregate = 0.84 cu.m.
Let's calculate the water volume in liters through the water/cement ratio for M20-grade concrete.
Water-cement ratio: mass of water to mass of cement in kg (1 kg water = 1 liter)
The water-cement ratio is taken between 0.4 to 0.6.
Volume of water
Water/cement=0.5
Volume of water = 0.5*8*50 (as 8 bags of cement in 1 cu.m. M20 concrete)
Volume of water: 200 liters
Let's calculate the cost of materials as per the district rate.
Cement: 8 bags at Rs. 700 = 8*700 = Rs. 5600
Sand: 0.42 cu.m. at Rs. 3319.61=0.42*3319.61=Rs. 1394.14
Aggregate: 0.84 cu.m. at Rs. 3319.61 = 0.84 * 3319.61 = Rs. 2788.47
Water: 200 ltr at 0.2 = 200*0.2 = Rs. 40
Total Cost of Materials = 5600 + 1394.24 + 2788.47 + 40
=Rs.9822.72
Workers Cost Analysis
Skilled Workers: 0.8 per Cu.m. M20 Concrete
Unskilled Workers: 7.0 per cu. m. M20 Concrete
Workers cost calculation as per Kathmandu district rate for fiscal year 2079/80.
Skilled workers: 0.8 at 1185.00 = 0.8 * 1185 = Rs. 948
Unskilled workers: 7 at 870.00 = 7*870 = Rs. 6090
Total Workers Cost = 948 + 6090 = Rs. 7038
Cost-hire of equipment and tools analysis:
Hire of Tools and Plant at 3% of unskilled workers = 3% of 6090 = Rs. 182.7
Total Cost = Cost of Materials + Cost of Workers + Cost of Tools and Plant
=9822.72+7038+182.7
=Rs. 17043.42
Contractor overhead and profit analysis
Contractor overhead and profit = 15% of total cost
=(15/100)*17043.42
=Rs.2556.51
Total Cost with Contractor Overhead = 17043.42 + 2556.51 = Rs. 19599.93
Summary of the Rate Analysis
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Machine used Concrete work of the superstructure, deck slabs, and beams, including the supply of material and haulage distance up to 30 m |
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PCC 1:1.5:3 (M20) for 1 cu.m. |
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Description |
Type |
Unit |
Quantity |
Rate |
Amount |
Remarks |
|
Workers |
Skilled |
MDay |
0.8 |
1185 |
948 |
|
|
Unskilled |
MDay |
7.0 |
870 |
6090 |
|
|
|
Materials |
OPC Cement |
Bags |
8 |
700 |
5600 |
|
|
Sand |
Cu.m |
0.42 |
3319.61 |
1394.24 |
|
|
|
Agg.(20mm) |
Cu.m |
0.84 |
3319.61 |
2788.47 |
|
|
|
Equipment |
Vibrator/Mixture |
- |
L.S |
3% of unskilled workers |
182.7 |
|
|
Sub-Total |
17043.42 |
|
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|
Contractor Overhead: 15% |
2556.51 |
|
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|
Total |
19599.93 |
|
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Others:
Following similar procedures and norms, you can calculate the cost estimate for M10, M15, and M25 grades of concrete too.
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